In conventional practice, microphone units comprising a function for converting inputted sounds to electrical signals and outputting the signals have been applied to various types of voice input devices (for example, see Patent Literature 1, 2, etc.). A voice input device is a device for converting inputted voices to electrical signals and processing the signals, and examples thereof include mobile telephones, transceivers, and other voice communication devices; voice recognition systems and other information processing systems that use techniques for analyzing inputted voices; audio recording devices; and the like.
In Patent Literature 2, for example, the applicants have disclosed a microphone unit that has a function for suppressing background noise and picking up only proximal sounds and that is suitable for a close-talking voice input device (e.g., a mobile telephone or the like). The microphone unit of Patent Literature 2 is configured as a bidirectional differential microphone unit, thereby achieving the function of suppressing background noise and picking up only proximal sounds.